Justin Sullivan/Getty Images Tech companies should seek to combat the spread of extremist propaganda by using their "vast" wealth to end the encryption of anonymous online messages, Britain's terror watchdog said today.

Max Hill QC, the independent reviewer of terrorism legislation, said that it would be a "good solution" to the problem of Islamist and other dangerous material online if postings could only be made by people whose identity was known.

He said the aim would be to make such "verification" checks in "nano-seconds" using new software. Mr Hill's comments came in an interview with the Evening Standard during which he also called for a review of sentencing for some terrorist offences which can currently result in short prison terms.

He said one reason was to keep pace with the impact of social media in provoking offences, which had occurred since much of the key terrorist legislation was passed.

Mr Hill's focus, however, was on how to counter the threat of terrorist propaganda online following police warnings about the increasing danger it poses.

Home Secretary Amber Rudd, who suggested most people don't need encryption.Isabel Infantes EMPICS Entertainment/PAHome Secretary Amber Rudd suggested that tech firms could face punitive new legislation if they fail to do more to remove extremist content.

However, Mr Hill warned against using "sledgehammer" new laws.

Instead, cooperation with tech giants such as Google and Facebook offered the best way forward, including the potential introduction of "verification" checks on social media users.

"A discussion I have had with some of the tech companies is whether it is possible to withhold encryption pending positive identification of the internet user," said Mr Hill.

"If the technology would permit that sort of perusal, identification and verification, prior to posting that would form a very good solution … and would not involve wholesale infringement on free speech use of the internet.

"I'm talking about a nano-second."

Mr Hill conceded that experts were divided as to whether such checks were feasible but that it was a debate "worth having."

On the threat of legislation, Mr Hill warned that action against the tech giants could backfire.

"To use a big stick to beat the big tech companies is going to obstruct the process of finding technical solutions to which smaller platforms will sign up," he said.

"It would not be an effective solution to the problem of online extremism simply to drive the criminal publishers of that material into dark spaces which neither the police nor anybody else can reach."

On sentencing powers, Mr Hill said that judicial discretion, including the ability to impose short jail terms, should be retained. But a review of maximum penalties for propaganda crimes and other offences was needed.

"We are seeing some very hard examples of radicalisation that is swift, online, and involves almost no face-to-face contact between radicalisers and those who are vulnerable to the extremist message," he said.